old rediscovered schematic

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MrDEB

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thinking about reviving this circuit seeing how my PCboard etching has improved and have all the parts.
BUT looking at the power supply, trying to figure out WHY it has an op amp for the supply. I recall I got the idea and schematic over at the headwise website but can't find reference to it for reason it was put into the circuit.
The FETs will not be needed.
thinking that with the two 9v batteries I should be able to construct a duel supply?
any input or suggestions
 

wow LM3916! i didn't think they still made that dinosaur!

the opamp in the PS ensures that you have a perfect split rail even if you have a week 9V and a fresh one.
 
I already have 14 of the LM3916s. Pickup 18 months ago when this project and another larger 5 band EQ/spectrum anmalizer were being designed etc. but never got to the build stage.
hopefully I have another opa551 for the power supply
 
MrDEB said:
hopefully I have another opa551 for the power supply
Click to expand...

While it is good to use common components throughout a design, there is nothing critical about the opamp in the power supply, if you dont have opa551, just about anything would do such as a TL071 or TL072, or even a 741 if you have one on hand.

JimB
 
its all surfasce mount except the lm3916's. pretty sure I ordered extras?
contemplated going with a split rail transistor supply. have schematic somewhere?
 
split rail power supply

second alternative if I don't have an extra smd op amp
Hopfully have the other op amps?
 

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Ubergeek63 said:
the opamp in the PS ensures that you have a perfect split rail even if you have a week 9V and a fresh one.
Click to expand...
It ensures that you don't wind up with a weak one and a fresh one. The +9V has a heavier load than -9V, due to to LM3916s and the LEDs. If you used the batteries directly, the +9V battery would always fail before the -9V. With the op amps, both batteries see exactly the same load.
 
MrDEB said:
second alternative if I don't have an extra smd op amp
Hopfully have the other op amps?
Click to expand...
That does nothing but waste power. If you eliminated the ground connection at the junction of the batteries it would sorta do what you want, but your supply impedances would be 4.7k each. Not a good thing.
 
The JFET clippers are a really bad idea. The intent is to minimize negative excursions on the outputs, and they will do that, but the short circuit output current of the op amps is ≈40mA, so they waste a lot of power. They also put an unnecessary 1-5mA load on the op amps during positive swings.
Furthermore, they aren't necessary. The PNP emitter followers will clip negative excursions.
You also don't need U2 and U3, and the OPA2134s are overkill. TL072 or TL074 would work just fine for any of the op amps.
 
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The jfets are only if the circuit is used with AC power. not here as two 9v batteries are used.
I found 8 - smd 741 op amps. got in a big box of stuff some localy gave me. LOTS of useful stuff like ribbon cables, headers, about 50 12khz crystals, numerious 2n3055 and 3054 transistors etc.
 
You can't use AC to directly power the circuit (as I'm sure you know). If you use an AC-DC converter (rectifier and regulator), the circuit will perform just as it would with batteries. The only reason I can see for the FETs is if you have AC-coupled input signals which swing above and below ground, but then I can't see why you would have anything else. This is for audio, isn't it?
 
yes you plug your I pod or ? into it, adjust the EQ and the analizer displays some eye candy.
 
Yeah, so you will always have an AC input, but you don't need the JFETs, because the PNP emitter followers provide the negative clip action. You don't need U2 and U3, because they are just buffers (voltage followers), and the preceding stages already have low output impedance.
 
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are you sure I don't need U2 and U3. they are the inputs to the lm3916's as well as the output to the head phones
I contemplated tapping the output to the headphones before U2 and U3 (outputs of U1 pins 7 & 14) so U2 and U3 act as a buffer so any noise from the display section won't interfer with the headphones.
NOTE I am not up on audio stuff so bear with me. Am surprised Audioguru hasn't chimed in.
 
MrDEB said:
Am surprised Audioguru hasn't chimed in.
Click to expand...

Hopefully, Mcquaky is doing Ok. You would think he would have.

Sometimes I in-vision Guru with several browsers open answering questions to several sites at one time.

Injecting his humor and his short quick comments to all the Audio Hopefulls and the like.

Sorta of a Santa Mcquacky.
 
You wouldn't have a problem with the display section interfering with your headphones. The only possible problem I could see is if you have low impedance phones that you like to run at painful sound levels. If that's the case, the OPA551's could go into the filter sections instead of the OPA4134. Or, you could just leave it as it is.
 
It is just two tone controls circuits and two LM3916 VU meters.
If it is biased differently and correctly then it needs only a single-polarity power supply or battery.

I agree that it uses too many opamps. The inputs of the peak detector transistor circuits do not cause audio noise. If your headphones are 8 ohms then ordinary opamps cannot drive them.
 
not aware of what the impedance of a pair of Ipod headphones are?
the original circuit was from the headwise website.
your guess is as good as mine unless someone can measure the impedance of Ipod headphones as I don't own an Ipod or other MP3 player.
 
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